For example, a typical unidirectional condenser microphone picks up sound from two directions, i.e., from the front and back of its diaphragm. Accordingly, the casing containing a microphone unit should have openings in its front and main walls.
In the vicinity of the openings in the main wall of the casing, a pathway is provided to send audio signals from the microphone unit to an impedance converter. In such a configuration, the vicinity of the openings in the main wall of the casing is susceptible to noise due to the electrostatic coupling in this pathway. To reduce the effect of the noise due to electrostatic coupling in the vicinity of the openings in the main wall of the casing, the microphone has an electrostatic shield, such as a metal mesh, at the openings.
The openings in the casing of the microphone require high electrostatic-shielding performance while effectively picking up sound. For this reason, the metal mesh strip is attached to the casing so as to entirely cover the openings while sufficient aperture is ensured. The metal mesh strip is composed of a cylindrical metal strip rounded along the main wall of the casing and fixed inside the casing with an adhesive or any other fixer.
Unfortunately, this metal mesh strip inside the casing barely covers the openings due to its variations in size and directional or positional misalignment inside the casing, leading to low electrostatic-shielding performance.
For example, Japanese Patent No. 5162484, hereinafter referred to as Patent Document 1) discloses a microphone that has a shield plate with tongues at both ends of the microphone in the longitudinal direction, and the tongues at one end overlap the tongues at the other end alternately to form a cylindrical shape.
The technique disclosed in Patent Document 1 barely overlaps tongues inside the casing and entirely covers the openings with the shield plate inside the casing, thereby leading to low electrostatic-shielding performance.